Pre-Engineered Steel Structures and Cold-Formed Steel Elements
The primary frame intervals of pre-engineered steel buildings are strengthened by auxiliary structural framing elements. For any main steel structure, these are known as secondary structurals and they can behave as flange bracing for the main structure system. They supplement the transfer of loading to the main frame and provide a key support role for the structure’s roof and walls. Purlins, or secondary roof members, help to structure the diaphragm of the steel roof. Girts, or secondary wall members, play an essential role in strengthening the walls of the building. Eave girts, eave struts, or eave purlins carry out the functions of both girts and purlins – the wall siding is supported by the webs and the roofing panels by the top flange.
Local buckling can occur with cold-formed steel. This develops when an element of the web and compression flange is broken down after certain stresses come into play. If an element fails, it will be unable to support its portion of the load. The overall support features in this area may also be damaged by distortional buckling, which involves a motion of the compression flange and the adjacent lip moving apart from its planned location. In cold-formed steel production, caution should always be employed in order to prevent any buckling.
The application of thin gauge element design is also unfavorably demonstrated in the web crippling process. This routinely occurs along the support attachments, where the optimal pressures exist. By disseminating the reaction force to the primary steel framework, bearing stiffeners at the supports help to ease this problem. All stiffeners are normally comprised of plates, channel pieces, or clip angles. A web crippling event break down will present a distortion of the purlin under stress atop the rafter. Due to the supporting qualities of the particular clip angle connected to the purlin, use of a bearing clip angle as a web stiffener will stop the purlin from distorting. From a “Z” purlin web, the load is transported by way of screws or bolts straight to the stiffener and directly from the stiffener to the rafter. Further securing of the purlin horizontally, if necessary, is attainable with alternative design procedures.
The secondary components used in steel building construction are largely formed through a cold-formed steel framing process. This pattern of steel assembly needs a great deal of time to fabricate. Extremely malleable materials are used, which can deteriorate from deformations under load. Its broader hot-rolled steel match will not have this problem.
By altering stress distribution in the cold-formed commercial grade steel framework course, torsional reliability can also be adversely affected. Even low amounts of stress can result in the buckling and consequential twisting and bending defeat of particular structural members. This problem can be rectified by introducing uniformly low compressive stresses upon the assembly or with the attachment of accessory support.
With regards to cold-formed frameworks where only certain locations of the bracing members are depended upon to handle compressive stresses, the concept of effective design width is necessary. Any effective design width calculation should have the maximum degree of stress used in the formula for effective design and manufacturing expectations.